Referring to FIG. 1, a schematic cross-sectional view of a conventional scanning apparatus 1 is illustrated. The scanning apparatus 1 comprises an optical reading head 10 therein. In the housing 100 of the optical reading head 10, a light source 101, a mirror set including plural reflective mirrors 102A˜102E, a lens 103 and an image sensor 104 are provided. During operation, the light emitted from the light source 101 is projected onto an object 11 to be scanned. The light reflected from the scanned object 11 is successively reflected by the plural reflective mirrors 102A, 102B, 102C, 102D and 102E, and then focused by the lens 103. The focused light is then imaged onto the image sensor 104 to convert the optical signals into analog electrical signals. In addition, the optical reading head 10 of the scanning apparatus 1 is driven by a driving device (not shown) so as to scan the whole object 11.
Please refer to FIG. 1 again. After the light source 101, the mirror set, the lens 103 and the image sensor 104 are mounted within the optical reading head 10, a magnification correcting procedure should be performed. By precisely adjusting the distance from the object 11 to the lens 103 (defined as an objective distance) or the distance between the lens 103 and the image sensor 104 (defined as an image distance), tolerance of magnification for the optical reading head 10 would be equal to or less than a preset value. The preset value is usually less than 0.5. As shown in FIG. 1, the reflective mirrors 102A˜102E of the mirror set are fixedly arranged within the optical reading head 10 and located in the optical path between the object 11 and the lens 103. Under this circumstance, the assembler may correct the magnifying power of the optical reading head 10 only by adjusting the position of the lens 103 relative to the image sensor 104 in the optical path. Since the distance between the lens 103 and the image sensor 104 is much smaller than that between the object 11 and the lens 103, it is difficult to precisely image the object 11 onto the image sensor 104 during the process of assembling the optical reading head 10 and reduce the tolerance of magnification. Therefore, it is desired to add a mirror adjustment mechanism to the optical reading head 10 so as to facilitate correcting the magnifying power of the optical reading head 10 in a simple and precise manner.
On the other hand, the mirror set or the image sensor 104, which should be precisely positioned, is readily sloped during the assembling process. In addition to the undesired sloping movement of the mirror set or the image sensor 104, the inherent imaging tolerance of the lens 103 also contributes to the sloping movement of the optical path for the optical reading head 10. As known, the assembler fails to overcome these problems by adjusting the position of the lens 103 or the image sensor 104.
In views of the above-described disadvantages of the prior art, the applicant keeps on carving unflaggingly to develop an optical reading head of a scanning apparatus according to the present invention through wholehearted experience and research.